Technical Field
The present disclosure relates to an apparatus for processing semiconductor wafers.
The disclosure particularly, but not exclusively, relates to an apparatus for carrying out a polymers removal process step and the following description is made with reference to this field of application for convenience of explanation only.
Description of the Related Art
As it is well known, a wafer is a slice of semiconductor material, such as a silicon crystal, used in the manufacturing of integrated circuits and other microdevices. The wafer undergoes many manufacturing process steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning in order to realize several integrated circuit thereon. Finally the individual integrated circuits are separated, during a dicing step, and packaged.
Among the different manufacturing process steps, one of the most important is the step of removal of polymers from the wafer surface.
The polymer removal process steps is commonly performed after a dry metal etching step. The polymer removal process step is used in many technologies, such as the manufacturing processes for realizing devices using gold metallization, for instance DMOS, GaN HEMT transistors, and in the following reference will be made to these manufacturing process only for sake of illustration.
In particular, the polymer removal process step is carried out using a cleaning solvent. The most commonly used solvent to remove polymers is the one known with the commercial acronym of EKC265™, a highly selective, hydroxylamine-based solvent for post-etch residue removal.
When handling the EKC265™ solvent one should exercise particular precautions, since it may cause burns and allergic skin reactions during a prolonged skin contact. Moreover, an inhalation of EKC265™ solvent may cause respiratory tract irritation and a prolonged or repeated exposure may cause difficulty in breathing, headache, nausea, vomiting, drowsiness, cyanosis and lung damage.
During the polymer removal process steps of wafers, a wet bench is used, wherein the wafer is dipped in the EKC265™ solvent during a fully automated process step.
A well known apparatus used for the polymer removing process on a metal layer is the so called Solvent Spray Tool (SST), which is produced by SEMITOOL and is used in the post etch polymer residual removal process to clean the surface of wafers.
The SST apparatus comprises a process chamber with a rotor to support a wafer carrier. The polymer removal process is managed by software, the chemicals, among which the EKC265™ solvent, being introduced automatically by spray nozzles having a flow rate capability which ensures uniform coverage to both sides of the wafers.
More in particular, mechanical and centrifugal forces are applied to the wafers which rotate in a closed chamber, thus assisting and enhancing the reaction of chemicals on the wafer surface.
The SST apparatus realizes a closed loop process control, wherein chemicals are continuously recycled and filtered.
More in particular, the polymer removing process performed by the SST apparatus comprises the following steps in sequence:                sprying the wafers with EKC265™ solvent;        spraying the wafers with isopropyl alcohol (also propan-2-ol, 2-propanol or the abbreviation IPA); and        rinsing the wafers with de-ionized water (DIW).        
In particular, the residue removal takes place where EKC265™ solvent is fed by means of suitable spray nozzles in a chamber wherein the wafers are housed, according to a pre-determined cycle of chemical re-circulation and wafer run. The re-circulation starts when the wafer run is over and the EKC265™ solvent is delivered to the chamber.
Then, isopropyl alcohol (IPA) is fed by the spray nozzles to the chamber. The isopropyl alcohol (IPA) is known to dissolve a wide range of non-polar compounds. Moreover, it is known that IPA is relatively non-toxic and evaporates quickly, being thus widely used as a solvent and as a cleaning fluid.
Finally, DIW is fed to the chamber for a rinse step of the wafers.
The polymer removal process performed by the SST apparatus also comprises a final step of blowing the wafers with nitrogen (N2) for drying them.
The SST apparatus advantageously is a full automatic system, an operator intervention being used only for loading and unloading the wafer carrier and to change the drums containing the chemicals. Also, the SST system allows to dry the wafers.
However, it should be noted that in the SST apparatus the chemicals are introduced in a same chamber, not preventing phenomena of water infiltration, for instance due to a faulty valve.
It is remarked that water contamination in EKC265™ solvent may cause the corrosion of the metal layers of the integrated circuits of the wafers.
It should be also noted that the known SST apparatus is not able to process samples having different shape and size than silicon wafers for which the wafer carrier is sized. However, the treatment of differently sized and shaped semiconductor products could be desired, for instance in case of prototype samples.